Now your going down a whole seperate part of fly fishing that not a lot of people venture Making your own leaders does give you complete presentation over your entire casting process, cheaper by the foot, but it will take some time and effort on your part to find the write formula for you. Making your own leaders lets you control presentation based on your casting style, weather conditions, water conditions and size/weight of the flies your throwing. On top of that your options are expanded with the hundreds of mono and flourocarbon lines on the market today to build your leaders.
If you find yourself throwing a certain size and type of fly most of the time, then making that best leader setup for you might not be a bad idea. But if your changing flies throughout the day based on the type of water your fishing, then you need to either change your tippet or change the entire leader, or neither and make it work. As you improve your casting, you'll just adjust to different flies (of near the same size/weight) using the same leader.
The only leaders I build are used for big top water flies for northern pike and bass. Streamers type patterns, I just use short pieces of straight mono/flouro, then tie on a wire tippet if chasing pike and musky. For trout I buy good quality leaders, then replace the tippet sections as needed. I'll changes the tippet sections based on the type of fly I'm throwing, make leaders longer if trout are wary, etc.
I would recommend staying away from making leaders for trout because you'll have less knots for less wind resistance and you'll enjoy it more just working the tippet section of leaders to build something that will work in your current water conditions. If you think the trout are being leader shy, then try switching to 7x or 8x tippet. Or even going with some 6x-8x flourocarbon tippet, though flourocarbon lines do not float as much as mono, but with such light line, I've never had problems using them on dry flies. For trout I usually start out with a 5x leader, 9' (@5lb). I carry 3x-8x tippet spools of mono, then 4x flouro and 7x flouro. My original leader will last quite a long time, obvisouly until it's too short from changing tippets or it start getting nicks and wind knots.
Here is a good rule of thumb, dividee your fly size by 3, ie a size 10 fly would need say a 3x or 4x. Now you might even need to drop to a smaller size like a 5x or 6x because the fish are being a little spooky. But then you must account for the size fish your expecting to catch and type of hook set your doing. Or you could even go with a 3x for better turnover, but then replace the last 2 feet with some flourocarbon.
The 60-20-20 rule is a good one to follow if building your own leaders. For trout leaders I would choose the butt section mono about .024 inches, then work down from there forming your leader. Some lines are more limp then others, stronger, stiffer and the whole gammat when it comes to choosing mono. For me I choose Trilene XT for all my pike and bass fishing because it's super tough, not to stiff and not to limp and has a little bit of stretch. I use P-Line flouroclear for tippet sections if the fish are being a little leader shy. For trout leaders, I like using the Rio leaders, then either use rio tippets or scientific angler tippets.
When I'm out with clients, I adjust the leaders alot during the beginning trying to the find one depending on the clients casting ability, the local weather conditions and type of flies were throwing. I hate to say it, but sometimes it's the line that causes some problems (not keeping it clean, has cracks/nicks, so the cast are just not up to par, creating more drag, etc). That is why I always bring 3 extra rods, even if clients bring there own.
Choosing the right size leader is part of the game every fly angler plays, you can make it as confusing as you want it to be.
Alright a little long and probably confused people more now
